Electric field responsive fluids

Abstract

In a fluid composition which is capable of exhibiting a substantial increase in apparent viscosity under the influence of an electric field and which is of the type wherein solid particles of a chemical substance are dispersed in an electrically non-conducting oleaginous vehicle, superior performance results when the chemical substance is a polymer containing acid groups, the polymer having a density not exceeding 1.8 and a specified minimum water absorbency.

I claim: 
     
       1. An electroviscous fluid composition comprising in dispersion in an electrically non-conducting oleaginous vehicle, a water-containing solid phase, said solid phase consisting essentially of particles of a polymer containing acid groups, having a density of not greater than 1.8 and a water absorbency such that a sample thereof after being allowed to equilibrate with air containing water vapor, loses at least 8% of its weight when heated to constant weight at a temperature which does not cause decomposition of the polymer, and regains at least 40% of this loss in weight when exposed to air at an ambient relative humidity of about 60% and a temperature of 20° C. 
     
     
       2. An electroviscous fluid composition according to claim 1, wherein the acid group or groups are selected from the group consisting of carboxylic acid, sulphate and sulphonic acid groups. 
     
     
       3. An electroviscous fluid composition according to claim 1, wherein said polymer is an addition polymer. 
     
     
       4. An electroviscous fluid composition according to claim 3, wherein said addition polymer is derived from at least one monomer which contains at least one acid group and/or at least one group which is convertible to an acid group after polymerization of said monomer. 
     
     
       5. An electroviscous fluid composition according to claim 4, wherein said group convertible to an acid group is an ester group. 
     
     
       6. An electroviscous fluid composition according to claim 4, wherein said monomer is selected from the group consisting of acrylic and substituted acrylic acids. 
     
     
       7. An electroviscous fluid composition according to claim 6, wherein said monomer is methacrylic acid. 
     
     
       8. An electroviscous fluid composition according to claim 5, wherein said monomer is an alkyl acrylate. 
     
     
       9. An electroviscous fluid composition according to claim 8, wherein said monomer is selected from the group consisting of methyl acrylate and ethyl acrylate. 
     
     
       10. An electroviscous fluid composition according to claim 4, wherein a further monomeric constituent of the copolymer is provided by a member selected from the group consisting of an olefin, maleic acid, maleic anhydride, vinyl acetate and N-Vinyl pyrrolidone. 
     
     
       11. An electroviscous fluid composition according to claim 3, wherein the polymer is a cross-linked polymer. 
     
     
       12. An electroviscous fluid composition according to claim 11 wherein the polymer is chemically cross-linked by means of a substance selected from the group consisting of divinyl benzene and diallyl ether.